Can can we change same icon size and color in dialer.
with a custom rom you can do it!
How to install custom rom and from where
How do one install custom rom
root your phone and install new ROM with twrp.
This is a missing function. Root your phone and install new ROM? This is not a solution.
[Official] Here's how to back up your OnePlus Device
by Gary C., 2018-02-12